Severing blade with beveled gripping edge

ABSTRACT

Square cuts are obtained in thermoplastic tubing and the like by means of closing cooperating gripping jaws on the tubing, which jaws have a leading cutting edge and an offset gripping edge which slopes back to an outer surface of the blade.

United States Patent Dixie E. Gilbert Bartlesville, Okla.

Aug. 18, 1969 July 27, 1971 Phillips Petroleum Company Inventor Appl.No. Filed Patented Assignee SEVERING BLADE WITH BEVELED GRIPPING EDGE[56] References Cited UNITED STATES PATENTS 1,617,511 2/1927 Balch 83/192,712,169 7/1955 Buttress...... 83/51 X 2,825,405 3/1958 Maass et al.83/623 Primary Examiner-James M. Meister Attorney-Young and QuiggABSTRACT: Square cuts are obtained in thermoplastic tubing and the likeby means of closing cooperating gripping jaws on the tubing, which jawshave a leading cutting edge and an offset gripping edge which slopesback to an outer surface of the blade.

8 Claims, 7 Drawing Figs.

US. Cl 83/176, 83/54, 83/170, 83/375, 83/465, 83/623 lnt.Cl 826d 7/02,B26d 7/08 Field 01' Search 83/19-21, 9,15,16,176,170, 623, 375, 382,456, 453, 465, 51, 54

SEVEIHNG BLADE WITH lElEVlELEb GRIFPHNG EDGE BACKGROUND OF THE INVENTIONThis invention relates to apparatus for severing thermoplastic tubingand the like.

In certain special applications, it is highly desirable to obtain asquare cut when severing pipe and tubing. For instance, in the formationof bottles and other hollow objects from preformed parisons, it has beenfound preferable to extrude a continuous length of tubing and thereaftercut this tubing into individual segments for subsequent blow molding. Itis apparent that at least the end of the parison which is to form theneck of the resulting article, particularly in the case of bottleshaving screw tops, must not be cut at an angle or else the cap will notfit properly. While it is possible to obtain a square cut with a saw,this entails certain disadvantages. Among these are the problems withsawdust" formed by the cutting operation, which is both a maintenanceproblem and an economic waste unless it is recovered and reused. Also,if the tubing is to be severed as it is extruded, elaborate means mustbe provided to move the saw blade axially along with the tubing until itis severed.

SUMMARY OF THE INVENTION It is an object of this invention to achieve asquare cut in severing a thermoplastic tube.

It is a further object of this invention to provide a more economicalmeans to sever pipe and the like.

It is yet a further object of this invention to provide apparatus togrip and sever a thermoplastic tube or the like.

In accordance with this invention, thermoplastic tubing or the like issevered by means of cooperating blades which have a sharp leading edgeand a gripping edge offset slightly from said sharp leading edge, saidgripping edge sloping back to an outer surface of said blade.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, forming a part hereofwherein like reference characters denote like parts in the variousviews, Fit}. 1 is a side elevational view of two cooperating blades inaccordance with the instant invention; FIG. 2 is a side elevational viewenlarged somewhat to show detail of one blade; FIG. 3 is a sideelevational view of a pmr of cutting blades having symmetricallydisposed gripping edges; FIG. 4 is a top view of the blades of FIG. ll;H6. 23 is a sectional view of blades similar to those of FIG. ll showinga different configuration of the severing and gripping area; PEG. 6 is aview of an alternate embodiment of the invention; and FIG. 7 is aperspective view of tubing severed with the apparatus of t3.

DESCRIlP'llUN UF THE EMBODlMENTS The cutting mechanism of the instantinvention can be used for severing thermoplastic tubular pipe, channel,and the like. While it will generally be utilized in the severing ofround tubular material, it can also be utilized for severing hollowelongated shapes Wl'iich are not cyunclrlcal, such as those havingsquare or triangular cross sections. The invention is applicable forsevering tubular material made of any thermoplastic material and isparticularly suitable for severing tubular material made of polymers ofat least one mono-lolefin having 2-8 carbon atoms per molecule and poly(vinyl chloride), more preferably polypropylene.

The tubing can be severed in accordance with the instant inventionimmediately after solidifying an extrusion by placing the severingmechanism downstream from the cooling bath of the extruder and severingthe tubing as it is extruded. Alternatively, the tubing can be severedinitially into sections of comparatively great length and stored andthereafter cut up into workpieces of the desired length.

The tubular material must be heated to a temperature sufficient toprevent the polymer from shattering, and yet not sufiiciently high thatit will be tacky or lose its shape. Particularly with polypropylene, itis essential to heat it to a temperature at which it will not shatter,this temperature for polypropylene being from 200-335 F preferably 290--320 F. Broadly speaking, the proper temperature would be that betweenthe temperature at which the polymer shatters and a temperature about520 below its crystalline melting point (or softening point in the caseof amorphous polymers). For PVC, a broad temperature of l50--320 F.,more preferably about 210- 260 F. is suitable.

In this regard, it is noted that quite surprisingly in accordance withthe instant invention, the tubing is severed without sealing, eventhough for many of the polymers, the temperature utilized is the same asis utilized in very similar operations involving sealing with anapparatus similar to that of the instant invention, except without thebeveled gripping edge.

The severing blades may close at any commercially feasible speed;generally, the blades will close during at a time interval of between0.01 and 5 seconds, preferably between 0.05 and 0.02 seconds.

The severing blades can be made of any suitable metal. A preferredmaterial is Vega steel hardened to a 59-6l Rockwell C hardness. In apreferred embodiment, the blades are so carried by the means utilizedfor advancing and retracting them, that when fully advanced, the bladesproject between I and 2 mils beyond the theoretical centerlineseparating the two blades. This accounts for slight inaccuracies inalignment and it has been found by experimental results that such anarrangement achieves a good cut in every in stance whereas, without theoverlap, a slight film may be left between the cutting edges of theblade members. It has been found by actual tests that blades impingingunder such an operation utilizing the Vega steel are surprisinglyresistant to dulling and can be operated for as much as a million cyclesor move without sharpening.

Referring now to the drawings, in FIG. 1 there is shown a pair ofmatching opposed severing blades 12. Arm means 114 is adapted toreciprocate said blades forward into engagement as shown in this FIGUREand backward to allow insertion of the tubular material to be severed.Stop means 16 is adjusted so as to allow the blades to move forward tothe desired extent, preferably to the point where cutting edge lb (seeFIG. 2) of each blade extends past the theoretical centerline separatingthe two blades a distance of 1 to 2 mils.

Referring now to FIG. 2, which shows blade 12 in greater detail, thisblade is shown to have a leading cutting edge lb and a gripping edge 20.Gripping edge 20 is offset slightly back from cutting edge Ml. A surface22 of blade 12 slopes back from gripping edge 20 to outer surface 24 ofblade 12, which in this instance is disposed in such a relationship thatsurface 24 is the top surface. As shown in the figure, this surfaceslopes back at an angle from a plane perpendicular to gripping edge 20at an angle of 20. This angle is critical to the operation of theinvention and must be within the range of 5-60, preferably within therange of l030. Surface M of blade 12 slopes back from cutting edge iiito outer surface 28 of blade 22. As shown in the drawing, this surfaceslopes back at an angle of 45 to a plane perpendicular to the cuttingedge. This angle is preferably within the range of 4060; however, it canbe as low as 30 and can be as high as that is, cutting edge l8 can beflush with bottom surface 2%. Between cutting edge 18 and gripping edge20, the blade is recessed to form recessfi tl.

As shown in FIG. 2, the distance from cutting edge to surface 2 3 is 62rolls with point 19 be ng 3i mils below surface, although these exactdimensions are not critical. Generally, the distance between edge lb andsurface will be about 40 to 200, preferably 50 to l00, mils.

The configuration described hereinabove is essential to the operation ofthe invention. it is essential to have a gripping edge '20 as opposed tosimply bringing two knife edges together. This is because if two knifeedges are brought together in a blade not having gripping edge such asthose represented by reference character 20, the tubing will twistslightly as it is being cut and thus an uneven cut will result. Theeffect of gripping edges 20 is to hold the parison square while it isbeing cut. A blade having a cutting edge and a gripping edge which isflush with the upper surface, such as is shown in the upper portion ofFIG. 6 results in a seal in many instances, for instance withpolypropylene at a temperature as much as 50 below the crystallinemelting point, a seal will result.

The discovery that beveling off the gripping edge will result in thetubing being severed and immediately opening back up without beingsealed was totally unexpected and is not completely explainable.Apparently, the upward component of force directed against the upperportion of the tubing by surface 22 causes the tubing to pull out of thesevering blades immediately on their closure just as would occur ifgripping edge 20 were not present. The length of surface 22, i.c., fromedge 20 to the point where it intersects surface 24 must be at least 10mils. Generally, it will be within the range of 10 to 100 mils,preferably 12 to 50 mils. In this way, the advantage of gripping edge 20to align the tubing is achieved without the disadvantage of it causingthe tubing to seal. For this reason, the angle of surface 22 to thehorizontal is critical. As stated hcreinabove, this angle must be withinthe range of 5-60, preferably l-30. It is apparent that as this angleapproaches 90, the configuration approaches thatshown in the upperportion of H6. 6, which configuration resr rlts in a seal rather thansevering without sealing.

When severing jaws 12 are fully extended as shown in FIG. 1, grippingedges 20 are in opposed relationship and spaced apart a dismnce which ispreferably within the range of 0.1 to 0.4, the wall thickness of theworkpiece. For instance, with a polypropylene tube of 0.125-inch wallthickness, these edges will be spaced apart a distance within the rangeof l350 mils, preferably about l825 mils.

The other angles are not critical and indeed, as shown in H6. 5, therecess can be in the from of a curve instead of the shape shown in theother FIGURES.

As stated hereinabove, the purpose of the gripping edge 20 is tomaintain the workpiece in alignment while the edge 18 is severing it. Asingle pair of gripping edges is sufi'rcient as shown in FIG. ll. Asquare cut is obtained using the apparatus of H6. 2 with no sealing ofeither the section of tubing disposed above the cutting edges or thesection disposed below. The section above the cutting edges is notsealed because of the beveled surface 22. The portion below is notsealed because there is no gripping edge at all to cause it to becompressed together and sealed.

However, while a single gripping edge is sufficient to hold the parisonin alignment, the severing blades 124 can have symmetricaliy disposedgripping edges above and below a cutting edge, each of said grippingedges having sloping surface 22a, as shown in PEG. 3.

FIG. 5 shows severing blades 12b wherein the recessed area is curved.

FIG. 6 shows an alternate embodiment of the instant invention wherein athermoplastic tubular length can be severed and the portion above thesevering line sealed to fonn a closed end parison and the portion belowthe severing line left open. In this figure, there is shown severingjaws 12c with cutting edges 18c. Below cutting edges 18:: are grippingedges 20c, each of which has a sloping surface 22c. This conf gurationis identical to that of FIG. I, and thus results in the tubing beingsevered, but the separated portion below the severing line opening backup as opposed to being sealed. Above cutting edge 180, however, isgripping edge 32 which does not have a beveled or sloping surface, butrather is flush with the upper or outer surface of blade 12c. With thisconfiguration, a portion of the thermoplastic material is trapped inrecess 30c and is compressed so as to form a seal so that the separatedportion of thc tube above cutting edge 18 is sealed. Utilizing thisapparcttiE, a continuous length of thermoplastic tubing can be extrudedand asthe blades are closed, parisons are formed having an open end anda closed end with no waste material being formed. i

FIG. 7 shows a section of tubular material which has been cut with theblade of FIG. 6. In this'FlGURE, the sections of tubing have been cockedat an angle to show the sealed upper portion and the severed andunsealed lower portion.

Of course, the spectacular results shown in FIG. 7 wherein one end ofthe parison is sealed and the other severed without sealing can only beaccomplished with certain materials operating at certain temperatures,for instance, polypropylene at a temperature in the neighborhood of290320 F. However, the invention has wide applicability to a wide rangeof polymers so far as the principal embodiment of utilizing the beveledgripping edge to effect severing without scaling is concerned. That is,with certain polymers and certain temperatures, blades such as is shownin MG. 6, while effecting a severing without sealing operation on thelower half, may effect only a partial seal or distortion of the upperportion.

EXAMPLE I Polypropylene hornopolymer having a density of 0.905 (ASTM Dl505-63T), a melt flow of2 (ASTM D l238-62T, Condition L), and acrystalline melting point of 450 F. was extruded into tubing having aninternal diameter of 0.8-inch and a wall thickness of 0.125-inch. Thetubing was cooled to room temperature and cut into 7-inch lengths. These7-inch lengths were heated to a temperature of 320 F. and severing jawsidentical to those shown in H65. 1 and 2 were closed upon a section ofthis tubing at a speed sufficient to give a closing time of 0.! of asecond. The distance between gripping edges 20 as the sealing bladeswere fully advanced was 20 mils. The tubing was cut square and cleanlyand both the severed section above and below the cutting edges poppedopen and immediately regained an essentially round configuration.

ldentical polymer heated to the identical temperature was placed betweenidentical jaws except that the upper edge of the gripping jaw was notbeveled, that is, the jaw had the configuration of FIG. 1 except thatsurface 22 extended up to where the gripping edge was flush with uppersurface 24. That is, this area had the configuration as shown in theupper portion of the jaw of FIG. 6. The severed section of the tubingabove cutting edge 18 was sealed sufficiently to give a watertight seal.

EXAMPLE ll Polyethylene was extruded into tubing of the same dimensionsas that of Example l and severed with an apparatus identical to thatused in Example l, that is, apparatus such as is shown in H0. K. Thetubing was heated to a temperature of about 5 below the crystallinemelting point. As in Exampie l, the tubing was severed without sealing.Similar tubing was formed from unplasticized poly(vinyl chloride) andsevered with an apparatus identical to that used in Example I, that is,as shown in F lG. l. This tubing was heated to a temperature of 220 F.The poly(vinyl chloride) tubing also was severed without sealing.

While this invention has been described in detail for the purpose ofillustration, it is not to be construed as limited thereby, but isintended to cover all changes and modifications within the spirit andscope thereof.

Iclaim:

1. Apparatus for severing a thermoplastic tubular workpiece comprisingin combination: a pair of cooperating matching blades, each of saidblades having a leading cutting edge, a gripping edge offset slightlyback from said cutting edge, a surface sloping back from said grippingedge at an angle of 5--60 from a plane perpendicular to said grippingedge to an outer surface of said blade; and wherein'said gripping edgeand cutting edge are spaced apart and separated by a recessed area.

2. An apparatus according to claim ll wherein said surface slopes backfrom said gripping edge at an angle of l0--30.

3. An apparatus according to claim 1 wherein said matching grippingedges are separated by a distance of 13-50 mils when in fully closedposition.

4. An apparatus according to claim 1 wherein a surfaces of said bladeadjacent said cutting edge on a side opposite from said gripping edgeforms an angle with a plane perpendicular to said cutting edge ofbetween 40 and 60.

5, An apparatus according to claim 1 comprising in addition a secondgripping edge disposed on the opposite side of said cutting edge, saidsecond gripping edge being offset slightly back from said cutting edge,said blade having a surface sloping back from said second gripping edgeat an angle of 560 from a plane perpendicular to said gripping edge to asecond outer surface of said blade, said second outer surface beingspaced parallel to said first outer surface, said second gripping edgebeing spaced apart from said cutting edge and separated by a recessedarea.

6. An apparatus according to claim 1 wherein said recesses area iscurved.

7. An apparatus according to claim 1 comprising in addition a secondgripping edge on the opposite side of said cutting edge from said firstgripping edge, said second gripping edge being offset slightly back fromsaid cutting edge, and separated therefrom by a recessed area, saidsecond gripping edge being flush with a second surface of said blade,said second surface being parallel to said first surface.

8. An apparatus according to claim 1 comprising in addition, means tomove said blades into and out of engagement, said means having stopmeans to stop forward movement of said blades at a point where saidcutting edge of each blade projects I to 2 mils past a centerlinebetween said blades.

1. Apparatus for severing a thermoplastic tubular workpiece comprisingin combination: a pair of cooperating matching blades, each of saidblades having a leading cutting edge, a gripping edge offset slightlyback from said cutting edge, a surface sloping back from said grippingedge at an angle of 5*-60* from a plane perpendicular to said grippingedge to an outer surface of said blade; and wherein said gripping edgeand cutting edge are spaced apart and separated by a recessed area. 2.An apparatus according to claim 1 wherein said surface slopes back fromsaid gripping edge at an angle of 10*-30*.
 3. An apparatus according toclaim 1 wherein said matching gripping edges are separated by a distanceof 13-50 mils when in fully closed position.
 4. An apparatus accordingto claim 1 wherein a surfaces of said blade adjacent said cutting edgeon a side opposite from said gripping edge forms an angle with a planeperpendicular to said cutting edge of between 40* and 60*.
 5. Anapparatus according to claim 1 comprising in addition a second grippingedge disposed on the opposite side of said cutting edge, said secondgripping edge being offset slightly back from said cutting edge, saidblade having a surface sloping back from said second gripping edge at anangle of 560* from a plane perpendicular to said gripping edge to asecond outer surface of said blade, said second outer surface beingspaced parallel to said first outer surface, said second gripping edgebeing spaced apart from said cutting edge and separated by a recessedarea.
 6. An apparatus according to claim 1 wherein said recesses area iscurved.
 7. An apparatus according to claim 1 comprising in addition asecond gripping edge on the opposite side of said cutting edge from saidfirst gripping edge, said second gripping edge being offset slightlyback from said cutting edge, and separated therefrom by a recessed area,said second gripping edge being flush with a second surface of saidblade, said second surface being parallel to said first surface.
 8. Anapparatus according to claim 1 comprising in addition, means to movesaid blades into and out of engagement, said means having stop means tostop forward movement of said blades at a point where said cutting edgeof each blade projects 1 to 2 mils past a centerline between saidblades.